1. Field of the Invention
The invention relates to a light emitting diode package, and more particularly, to a light emitting diode package having scatterer supported wavelength converters embedded in a molding material and having superior illumination uniformity and manufacturing convenience.
2. Description of the Prior Art
Recently, the new application fields of high illumination light emitting diodes (LEDs) have been developed. Different from a common incandescent light, a cold illumination LED has the advantages of low power consumption, long device lifetime, no idling time, and quick response speed. In addition, since the LED also has the advantages of small size, vibration resistance, being suitable for mass production, and being easily fabricated as a tiny device or an array device, it has been widely applied in display apparatuses and indicating lamps of information, communication, and consumer electronic products. The LEDs are not only utilized in outdoor traffic signal lamps or various outdoor displays, but also are very important components in the automotive industry. Furthermore, the LEDs also work well in portable products, such as cell phones and backlights of personal data assistants. The LED has become a necessary key component in the very popular liquid crystal display because it is the best choice when selecting the light source of the backlight module.
A common light emitting diode package comprises a light emitting diode device. The light emitting diode device is a light emitting device fabricated on a semiconductor material and has a positive terminal and a negative terminal. When a forward voltage is applied between the two terminals, the remaining energy caused by recombination of electrons and holes is excited and released in a form of light although only a small amount of current flows into the PN junction. The electrical energy is thus transferred to optical energy. When a reversed voltage is applied between the two terminals, the PN junction is reverse biased. Therefore, minority carriers are difficult to inject so that the light emitting diode device will not illuminate. When light is emitted from the light emitting diode device, a series of procedures including diffusing, reflecting, and mixing proceed in a molding material to generate satisfactory tone and brightness. Therefore, the geometry of the package and the selection of the molding material are important parameters when designing the light emitting diode package.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art lead type light emitting diode package 10. As shown in FIG. 1, the prior art lead type light emitting diode package 10 comprises a light emitting diode chip 12, a mount lead 14, and an inner lead 16. The mount lead 14 further comprises a cup 18. The mount lead 14 is used as a negative electrode, and the inner lead 16 is used as a positive electrode. The light emitting diode chip 12 is disposed in the cup 18 of the mount lead 14. A P electrode and an N electrode (both are not shown in the figure) of the light emitting diode chip 12 are connected to the mount lead 14 and the inner lead 16, respectively, by conductive wires 22. The cup 18 is filled with a molding material 24 for encapsulation. A plurality of fluorescent materials (not shown) are spread in the molding material 24.
When light beams are emitted from the light emitting diode chip 12, portions of the light beams are absorbed by the fluorescent materials in the molding material 24 to excite the fluorescent materials such that light beams in another wavelength are generated. The fluorescent material thus functions as a wavelength converting material. By subtly mixing the light beams emitted from the light emitting diode chip 12 and light beams converted by one or a plurality of fluorescent materials, mixing light beams of white color or another color are eventually emitted. In order to obtain white light beams or mixing light beams with homogeneous tone by perfectly mixing light beams of different colors, the molding material 24 should not only comprise the fluorescent materials but also comprise many scattering materials (not shown) spread in it. Due to the existence of the scattering materials, the light beams emitted from the light emitting diode chip 12 are repetitively scattered and diffused to increase the emitting angle of the light beams emitted from the light emitting diode chip 12. Therefore, light beams having abrupt intensity are inhibited to become soft. In addition, the mixing light beams become very homogeneous. Furthermore, various additives for different objectives may be included in the molding material 24, according to practical requirements.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of a prior art chip type light emitting diode package 50. As shown in FIG. 2, the prior art chip type light emitting diode package 50 comprises a light emitting diode chip 52 and a casing 54. The casing 54 further comprises a positive metal terminal 56 and a negative metal terminal 58. The positive metal terminal 56 is used as a positive electrode, and the negative metal terminal 58 is used as a negative electrode. The light emitting diode chip 52 is disposed in a recess 62 of the casing 54 and is on top of the positive metal terminal 56. A P electrode and all N electrode (both are not shown in the figure) of the light emitting diode chip 52 are connected to the positive metal terminal 56 and the negative metal terminal 58, respectively, by conductive wires 64. The recess 62 is filled with a molding material 66 for encapsulation. A plurality of fluorescent materials (not shown) are spread in the molding material 66.
When light beams are emitted from the light emitting diode chip 52, portions of the light beams are absorbed by one kind or more than one kind of the fluorescent materials in the molding material 66 to excite the fluorescent materials such that light beams in another wavelength or light beams in other wavelengths are generated. By controlling the mixing between the light beams emitted from the light emitting diode chip 52 and the light beams converted by the fluorescent materials, light beams emitted from the chip type light emitting diode package 50 become light beams of white color or another color. Similarly to the lead type light emitting diode package 10 shown in FIG. 1, the molding material 66 should not only comprise the fluorescent materials, but also should comprise many scattering materials (not shown) spread in it in order to obtain mixing light beams of white color or another color with homogeneous tone, by perfectly mixing light beams of different colors. The mixing light beams thus become very homogeneous. In addition, various additives for different objectives may be included in the molding material 66, according to practical requirements.
Both the lead type light emitting diode package 10 and the chip type light emitting diode package 50, as mentioned previously, can achieve the objective of color mixing so that light beams of white color or another color are generated. However, the lead type light emitting diode package 10 and the chip type light emitting diode package 50 have different packaging structures. Actually, different packaging structures will result in different illumination performance. No matter what kind of packaging structure is adapted, the final objective is to produce products having satisfactory whole tone homogeneity and brightness uniformity. When considering the uniformity issue, the molding material 24, 66 themselves become important points. Especially, whether the scattering materials in the molding materials 24, 66 can provide the products with superior uniformity becomes very important.
In the prior art, the fluorescent materials, the scattering materials, and other materials are usually mixed in a resin used for packaging. Therefore, all of these materials are embedded into the molding materials 24, 66. However, this method causes various problems when performing the mixing procedure. When different material particles are mixed in the resin used for packaging, an inhomogeneous mixing phenomenon tends to occur because different material particles have different weights, different shapes, different physical properties, and different chemical properties. Particularly, the scattering materials, usually in the form of particles or bubbles, always have this problem. Once this inhomogeneous phenomenon occurs, the whole tone homogeneity and brightness uniformity are affected.
Therefore, it is very important to develop a new molding material. The inhomogeneous phenomenon should be eliminated when this molding material is applied to different packaging structures. In addition, the fabrication should be convenient. The processing complexity should not be increased.